1. Field of the Invention
The present invention relates to a charged particle beam pattern writing method and apparatus, and more particularly to a method and apparatus for correcting by a beam dose a pattern size variation amount which takes place due to the so-called proximity effect and the partial opacity like a dark hazy veil or “fog,” which occur due to electron beam pattern writing by way of example, and a pattern size variation amount which takes place due to loading effects during pattern formation after the electron beam writing.
2. Related Art
A lithography technique which bears advances in miniaturization of semiconductor devices is a very important process which is only a process for generating patterns among semiconductor fabrication processes. In recent years, with an increase in integration density of LSI, the circuit line width required for semiconductor devices is decreasing year by year. In order to form a desired circuit pattern for these semiconductor devices, an original image pattern (called a reticle or a mask) of high accuracy becomes necessary. Here, an electron ray (electron beam) pattern writing technique inherently has excellent resolution and is for use in the manufacture of high-accuracy original image patterns.
FIG. 21 is a conceptual diagram for explanation of an operation of one prior known variable-shaped electron beam lithographic apparatus.
In the variable-shaped electron beam lithographic apparatus (electron beam or “EB” pattern writing apparatus), pattern writing is performed in a way which follows. In a first aperture 410, a rectangular or oblong opening 411 for shaping an electron ray 330 is formed. Additionally in a second aperture 420, a variable shaping opening 421 is formed, which is for shaping the electron ray 330 that passed through the opening 411 of the first aperture 410 to have a desired rectangular shape. The electron ray 330 which was emitted from a charged particle source 430 and passed through the opening 411 is deflected by a deflector and then passes through part of the variable shaping opening 421 to fall onto a workpiece 340 that is mounted on a stage. The stage moves continuously in a predetermined one direction (for example, X direction). More specifically, a rectangular shape that can penetrate both the opening 411 and the variable shaping opening 421 is written in a writing region of the workpiece 340 which is mounted on the stage that moves continuously in the X direction. A technique for forming any given shape by letting a beam pass through the opening 411 and variable shaping opening 421 is called the variable shaped beam (VSB) scheme.
When irradiating an electron beam onto a workpiece such as a mask with a resist film deposited thereon, several factors which fluctuate the size of a resist pattern are present, such as proximity effect and fogging. The proximity effect is a phenomenon that electrons irradiated are reflected at the mask and again radiate the resist, an influence range of which is approximately ten-odd μm. On the other hand, the fogging is a multiple scattering-induced resist irradiation phenomenon that back-scatter electrons due to the proximity effect behave to jump out of the resist and scatter again at the lower plane of an electron lens barrel and then reradiate the mask. The fog covers a wide range (several mm to several cm) when compared to the proximity effect. Both the proximity effect and the fog are phenomena for reradiation of the resist, and correction techniques for correcting such factors have been studied until today (for example, refer to JP-A-11-204415). Miscellaneously, a scheme for correcting a loading effect, that is, a size variation caused by a light shield film to be etched in the case of etching such light shield film or the like of a lower layer with a formed resist pattern being as a mask, is well known (for example, see Japanese Patent No. 3680425).
Additionally, in order to correct these proximity and loading effects, an entire circuit pattern is divided into global loading-effect small blocks of a square shape with each side of 500 μm, proximity-effect small blocks of a square shape with each side of 0.5 μm, and micro-loading-effect small blocks of a square shape with each side of 50 nm, respectively, followed by influence degree map preparation. A description as to a technique for calculating a dose for pattern writing by use of a dose (fixed value) capable of properly writing a circuit pattern with predetermined area density of 50% and a proximity effect influence value α map plus a proximity effect correction coefficient η map obtained from a loading effect correction value ΔCD is found in bulletins (for example, see JP-A-2005-195787).
As stated above, in charged particle beam image writing which typically includes electron beam lithography, in cases where an electron beam is irradiated onto a workpiece such as a mask with a resist film deposited and coated thereon, those factors that vary resist pattern sizes exist, examples of which are the proximity effect and the fog. Due to this, for example, upon writing of a pattern which is required to have its accuracy on the order of magnitude of nanometers (nm), problems occur as to generation of an uneven distribution for the finished size of a written pattern due to the influences of the proximity effect and fog. Furthermore, a size variation called the loading effect can take place after the pattern writing. Examples of such loading effect include, but not limited to, a development loading effect of resist film, Cr-loading effect at the time of etching chromium (Cr) that becomes a light shield film underlying the resist film, and a loading effect occurring due to pattern size variations during chemical mechanical polishing (CMP) in wafer manufacturing processes.
On the other hand, in the electron beam pattern writing, further enhanced uniformity of the line width within a mask surface is required with advances in miniaturization of pattern line width. In the case of correcting the above-stated proximity effect or the like by the dose of a beam, a correction quantity is calculated by use of a model equation. However, such the model equation has a correction residual difference. And, mask in-plane size variations occurring due to such the proximity effect correction residual difference and fog plus loading effect are about 1 nm/mm, which is moderate when compared to the proximity effect—a variation amount is about 10 to 20 nm. This mask inplane size variation is generated by resist species, resist thickness, resist deposition apparatus or method, post-exposure baking (PEB) apparatus or method, development apparatus or method, etching apparatus or method and others. Hence, a case takes place where size variations due to the correction residual difference are no longer negligible depending upon these resist species, resist thickness, PEB, development irregularities, etc. In addition, in the correction of size variations due to the fog and the loading effect also, achievement of higher accuracy is desired.